It still remains unclear to me how letting users opt out of making Twitter $0.55/month by giving Twitter, say, $4.95/month is a bad idea. OK, so the advertising rates go down... so what? Advertising rates are not what a business is trying to optimize, revenue is.
Up to this point, the counter to this argument was basically "Well, what Twitter's doing is obviously working for them". But that's not quite as strong as it used to be now. How much money did Twitter leave on the table? It is, sure, possible that it would have been a net loss for them. But now I think a fresh look must be taken at the possibility that it would have been enough of a net gain to ensure their indepedence.
Plus one must consider the second-order effects of receiving subscription revenue. Might they have created a different and more valuable service to their customers and made even more as a result? Advertising-based businesses face the intrinsic paradox of trying to serve two customer bases at once who have somewhat opposed interests. (Even ignoring the socially corrosive influence of advertising incentivizing our smartest people to build the most powerful spying networks in history.) It is still not determined to my satisfaction that that is a stable business plan in the modern era.
One possible salutatory effect of Twitter's demise could be making the idea of subscriptions reasonable again. If even Twitter can't monetize entirely on advertising, who else can? Even Google and Facebook may be surprisingly fragile to a disruption in the advertising space, which is nominally not actually their business (even though of course it is). (The most likely disruption would be the continuing growth of ad-blocking software, but there's also the black swan possibilities as well.)